Loudspeaker magnet structure and method of assembling same



NOVL 28, 1967 w, os 7 3,354,541

LOUDSPEAKER MAGNET STRUCTURE AND METHOD OF ASSEMBLING SAME Filed June 4,1965 J I N VEN TOR.

BY john 41/ 6051220 A TTORNEY v Patented Nov. 28, 1967 3,354,541LQUDSPEAKER MAGNET STRUCTURE AND METHOD OF ASSEMBLING SAME John W.Gosma, Kokomo, Ind, assignor to General Motors Corporation, Detroit,Mich, a corporation of Delaware Filed June 4, 1965, Ser. No. 461,285 2Claims. (Cl. 29607) This invention relates to loudspeaker magnetstructure and the method of assembling the same.

The majority of current loudspeaker assemblies utilize permanent magnetstructures to provide the field in which the voice coil is suspended andin which it moves to drive the diaphragm connected thereto to create andreproduce sound. Since stereo and multiple speaker outlets from a givenreceiver are now more common loudspeaker production is high and cost isan important factor. One further impetus to speaker production is due tothe introduction on the market of stereo systems for automotive use thatrequire four speakers.

It is an object in making this invention to provide a unitary magnet andcasing assembly that is low in cost and simple to assemble with theframe for the speaker.

It is a further object in making this invention to provide a novelmethod of forming a magnet and casing for a loudspeaker through theapplication of a strong magnetic field causing the casing to wrap aroundthe magnet and form a compact unitary assembly.

With these and other objects in view which will 'become apparent as thespecification proceeds, my invention will be best understood byreference to the following specification and claims and theillustrations in the accompanying drawings, in which:

FIGURE 1 is a side elevational view of a loudspeaker assembly embodyingthe invention, parts being broken away and shown in section; and,

FIG. 2 is an exploded view showing the parts of the magnet assembly inspaced relation.

The basic drive unit in this instance is formed of a ceramic magnet 2having a top pole plate 4 and a bottom pole plate 6. These magnets maybe made of hard ferrites and are rather brittle requiring care inapplying the housing or they might be cracked. The magnet 2 is ofannular form having a central opening 8 therein. It is proposed toencase this basic assembly of the magnet with its top and bottom poleplates in a casing or housing of aluminum and then applying a strongmagnetic field to cause the casing to wrap tightly around thesubassembly to form a complete unitary member. Such a casing 10 is shownin the form of a cup having cylindrical side walls and a bottom surfacebut an open top. If it were attempted to assemble the magnet within thecasing by folding over the upper edge either mechanically or by applyinga strong magnetic field through the use of such a device as aMagneformer the ceramic magnet might be cracked. It is, therefore,necessary to apply some lining shock absorbent material to protect thesame.

It has been found that a polyvinylchloride material works well in thisinstance and a layer of such material 12 is shown in the bottom of thecup or casing 10 in FIG. 2. The amount of polyvinylchloride materialused should be sufficient to surround the magnet on the sides and extenda short distance out over the top edge in the final assembly. The casing10 is, therefore, first filled to the desired point with thepolyvinylchloride material or some similar material which iselectrically insulating and will provide shock proofing. The lower plate6, the magnet 2 and the upper plate 4 are then placed in the casing insequence and properly located one upon the other. By slight pressurefrom the top the polyvinylchloride material will be forced up around theedges of the magnet parts and out over the top corner for a shortdistance to insulate and mount the magnet and poles. This subassembly isthen placed in an oven at an elevated temperature and cured at, forexample, 375, the temperature being determined by the material beingused. This sets the polyvinylchloride so that it becomes rubbery andholds the magnet assembly in place.

This assembly is now placed in a Magneformer which is a well knowncommercial device capable of applying a strong magnetic field to deformmaterial through discharge of a condenser. Upon actuation of the devicethe top edge of the casing 10 is folded in tightly over the magnet, asshown at 26 in FIG. 1, in a quick and single action to make a permanentmagnet unit for a loudspeaker.

As shown on the drawing, the lower plate 6 has a central opening 14which may be internally threaded and into which may 'be screwed a shortstud 16 integral with a central core member 18. This is inserted intothe central aperture to form a gap with the upper plate and an apertureinto which the voice coil 20 of the speaker may project and in which itis supported. The top plate 4 of the speaker is also provided with aseries of regularly spaced rivets 22 which when brought intojuxtaposition with the frame 24 of the speaker are adapted to projectinto mating openings therein and then peened over to secure the magnetunit to the speaker frame. These could, of course, be drilled out andthreaded and screws could be used for securing the unit as well as theriveted members.

It will be obvious that this is a very simple, fast and inexpensivemanner in which to quickly form magnet assemblies for loudspeakers andto assemble the same to loudspeaker frames.

What is claimed is:

1. A method of making a permanent magnet assembly including the steps oftaking a hollow deformable casing, filling it partly with an uncuredinsulating plastic, placing the parts forming the magnet and poles insequence in the casing, pressing the parts down to displace theinsulating plastic causing it to flow up around and slightly over theperipheral edge of the top of the same, applying heat to the assembly tocure the plastic material allowing the same to cool, applying an intensemagnetic field to distort the case and fold it in on the magnetsubassembly, the cured plastic protecting the magnet in the process.

2. The method as claimed in claim 1 in which the magnet is a ceramicmagnet that is brittle and the uncured insulating plastic ispolyvinylchloride.

References Cited UNITED STATES PATENTS 2,943,359 7/1960 Sussman 17452.6X 3,214,511 10/1965 Franklin 29-421 X 3,251,015 5/1966 Denham 17452.6 X

JOHN F. CAMPBELL, Primary Examiner. C. E. HALL, Assistant Examiner.

1. A METHOD OF MAKING A PERMANENT MAGNET ASSEMBLY INCLUDING THE STEPS OFTAKING A HOLLOW DEFORMABLE CASING, FILLING IT PARTLY WITH AN UNCUREDINSULATING PLASTIC, PLACING THE PARTS FORMING THE MAGNET AND POLES INSEQUENCE IN THE CASING, PRESSING THE PARTS DOWN TO DISPLACE THEINSULATING PLASTIC CAUSING IT TO FLOW UP AROUND AND SLIGHTLY OVER THEPERIPHERAL EDGE OF THE TOP OF THE SAME, APPLYING HEAT TO THE ASSEMBLY TOCURE THE PLASTIC MATERIAL ALLOWING THE SAME TO COOL, APPLYING AN INTENSE